Light, particularly the sunburn spectrum (UVB, 280-320nm), has been implicated as an etiologic agent in the induction of skin tumors in animals and man. We have shown that the administration of carotenoid pigments to patients with erythropoietic protoporphyria can ameliorate the light sensitivity associated with this disease, and that the administration of these pigments to normal volunteers was found to have slight but statistically significant action in delaying the appearance of erythema caused by the sunburn range. We have also found that phytoene, a precursor pigment having absorption maxima in the sunburn range, significantly decreased the erythemal reaction in guinea pigs exposed to this radiation. In addition, we and others have shown that carotenoid pigments can inhibit the formation of free radicals which have been implicated in photocarcinogenesis. Therefore, we propose to study the effect of the systemic administration of beta-carotene, phytoene, and other carotenoid pigments on the development of skin tumors induced by sunburn radiation and topical carcinogens in hairless mice. We have establised dosage levels and routes of administration which lead to significant accumulation of beta-carotene and phytoene in the skin of hairless mice, with no apparent toxicity. Methods already well-documented in the literature for the induction of skin tumors by sunburn radiation and topical carcinogen application will be used. Groups of hairless mice will be given carotenoids and appropriate placebos, and blood and skin levels of the pigments will be allowed to reach saturating levels before the tumor induction program begins. The mice will be observed for the development of skin changes and tumors. Tumors will be studied histologically and graded. Blood and skin carotenoid and vitamin A levels will be measured. The results of statistical analyses on the numbers of tumors and the time of tumor induction in the various groups of mice will indicate whether the systemic administration of carotenoids has any significant effect on tumor induction.